1. Field of the Invention
The subject invention relates to a disc brake system, and more specifically to a disc brake system that allows discs to freely slide axially when a braking force is applied to the disc.
2. Description of the Prior Art
Various disc brake systems are known to those of ordinary skill in the art. Currently, production vehicles such as automobiles often have spot-type disc brake systems that have a fixed disc and a caliper configuration with an inboard piston and cylinder operated by hydraulic fluid. The caliper is bolted to a suspension member either forward or rearward with respect to a vertical plane through a wheel axle and includes a slidable bridge sliding on pins with an outer brake, or friction, pad on the outboard end of the bridge. Operation of the brake pedal forces the piston outwardly to engage and to slide an inner brake pad along the bridge into frictional braking engagement with the inner side of the fixed disc, which is rigidly fixed to a hub on which the wheel is mounted. A reaction force on the slidable bridge causes it to slide on the pins and force the outer brake pad tightly against the outer side of the fixed brake disc. Deceleration of the clamped disc and its associated hub and its attached wheel thereby decelerates the vehicle. As the piston is forced to slide to engage the brake pads with the fixed disc, an internal O-ring seal between the cylinder and the piston is compressed, and energy is stored therein which is released, when the braking fluid pressure is relieved, to slide the piston in the reverse direction to its off brake position in the cylinder.
The above-described disc brake system is commonly referred to a conventional, fixed disc brake system because the system has a disc that is fixed to a hub of a wheel. Previously it was believed that slidable brake disc systems were unable to meet the rigorous, demanding criteria to the satisfaction of automobile manufacturers or suppliers. Vehicle manufacturers and brake suppliers undertake the risk of product liability lawsuits or product recalls and, therefore, are reluctant to adopt a new braking system unless it has superior qualities such as improved cost, weight, efficiency, longevity or other qualities relative to the standard fixed disc brake
Generally, the fixed brake disc systems are quite heavy and a reduction in weight is a desirable goal for the slidable disc brake system. In addition to size, cost and weight, there are the criteria of efficiency, proficiency, and longevity. Brake wear is a longevity problem and a longer brake pad life and brake disc life are desired by vehicle manufacturers which are increasingly providing long term service warranties for their vehicles, as well as for the vehicle owner who ultimately pays for brake replacement in one manner or the other. Still another problem is that some fixed disc brake systems have noise problems which are cured to a certain extent by the addition of noise suppressors, which add to the size, weight, and cost of the system. Brake systems must be free of rattles and should be free of noise. In addition to above, there also may occur a “feel” problem where the driver experiences a long or deep pedal depression when operating the brakes.
Another common disc brake system is referred to as sliding brake disc system. It is to be appreciated that in the sliding brake disc system, the disc must slide axially on the hub between an off-brake position, where the residual torque should be low and a braking position where the torque is high, and then return to the off-brake position to reduce the residual torque. The sliding connection between the brake disc and hub must be free to move despite being subjected to corrosive conditions and over a long period of use. If either disc is not able to freely slide, the system will not meet braking expectations. The slidable brake disc must not be noisy or squeal under low and high temperature conditions, and it must not wobble or generate dust or produce vibrations that the driver can feel or hear. The caliper system for sliding brake systems incorporates the piston that pushes an inboard disc into an outboard disc which generates four friction surfaces.
Prior sliding brake systems have included spline grooves oversized relative to a size of the disc teeth inserted into the grooves and spring devices where mounted on the hub to push the discs to rotate a driving side, flank of each tooth into mating engagement with a flank of the oversized spline groove. The oversized notches were used to prevent the previously heated and now cooled disc from jamming in the splines. To eliminate “knock back” and chattering, springs were inserted into the spline notches to bias the spline flanks on the disc and hub into engagement with one another. Such designs do not provide a good drive connection between the discs and the splined hub. The clearance between the hub and disk is a design problem, too much clearance will result in chatter during certain driving conditions and minimal clearance will result in a binding condition. Another issue encountered by these systems is that road debris, such as dirt, sand, or rocks, may lodge in the splines and interfere with the sliding of the discs.
From the foregoing, it will be seen that there is a need for a better, slidable disc mounting system that is more efficient and that does not generate noise or squeal as the discs expand at high temperatures and that does not wobble at high braking loads.